Just to add to this thread...I discovered a bug similar to one mentioned here where iMovie started appending 1, 2, etc. to volume names.
I had external drives named Media Library Volume 1, Media Library Volume 2, etc.
This worked fine in iMovie 08.
In iMovie 09, the Event library had no problem with these volume names. However, the iMovie Project Library was not able to deal with these volume names. The ability to move projects to an external drive is a new feature in iMovie 09, and they appeared to screw it up. The Project Library is limited to volume names of about 8 to 10 characters, while the Event Library can handle much longer volume names. This is why it randomly appends a 1 to a volume name like Media Library Volume 1 1, because it only reads "Media Library" and reads that there are four other drives with the same name.
I fixed this by a tedious process of moving all my events to a newly reformatted drive with a short volume name (Media 1, Media 2, etc.) I had to repeat this 4 times to get everything.
If the fixes mentioned in this thread work, then do that rather than my tedious way.